Video RAM is for the graphics card to store textures and stuff for quick and easy access. It's incredibly important to graphics intensive titles, more so then system RAM, and cannot be skirted.

Now whether or not you have enough depends on what the 256mb minimum means. Is that what it needs to run topped out? Optimum? Or minimum? If its minimum you're ***, if its optimum performance you can MAYBE get away with it, but I doubt it.